A huge number of oil or natural gas drilling rigs are currently being dismantled and this will result shortly in the need to remove numerous pipelines connecting these installations to dry land.
At present specific recovery systems are not envisaged and therefore the costs generally appear to be very high. In fact, the alternative solutions which hitherto may be taken into account envisage on the one hand the use of teams of underwater divers for cutting the pipes at depth and then the use of recovery means controlled from the surface on a special boat. This type of working method, which is not particularly recommendable owing to the increasing exposure of the underwater workers to risks, is time-consuming and involves decidedly high costs, attributable mainly to the use of numerous specialised workers who only occasionally work together as a team. With this method, in fact, it is possible to recover daily only a few sections of pipe each of about 24 meters length, with a relatively high cost per section.
Another possible solution for the removal of underwater pipelines involves the use of the same ships used to lay the pipes. These ships, which are highly specialised, are very limited in number and it is unlikely that they will be immediately available in the operations zones; this system, although it is much faster, since these ships are able to recover up to 100/200 sections per day, is nevertheless advantageous only in the case where pipelines of considerable length must be removed, since getting to the site and the daily cost of a pipe-laying ship involve particularly high costs.
The object of the present invention is therefore to provide a method for removing underwater pipelines which allows the dismantling of lines also of limited size at a reasonable cost. In order to achieve this type of result, it is necessary for the method to use a type of boat which is widely available and has a substantially small size compared to the operation performed, typically a supply vessel of about 60-70 meters length, and for cutting and removal of the underwater pipelines to be performed without the intervention of any underwater divers.